Conventional foldaway or breakaway mirrors used on the exterior of motor vehicles which rotate about a central spigot require a spring element to keep the mirror stable in a drive position. It is necessary to prevent vibration of the mirror caused by motion of the motor vehicle and wind passing over the mirror.
The same spring element that provides the stability can also, via a detent system, provide a torque to resist accidental displacement of the mirror head under small forces but under large forces the detent arrangement and the spring element force can be overcome to allow the mirror case to rotate about the spigot. This is done primarily to protect the mirror from damage, to protect the third party object that collides with the mirror from damage or to reduce the overall width of the vehicle.
The use of a spring element loaded to prevent vibration and to provide a torque to resist accidental displacement is necessary for both manual fold mirrors and many power fold mirrors. It is independent of the construction of a spigot, whether that be integrated, bayonet or the like, and it is also independent of the detent system used. It is also independent of the type of construction or assembly system used.
A spring used with a preload and detent system for a motor vehicle external mirror goes through a number of different stages during assembly and operation. First the spring has a free length or maximum extension. Next the spring is preloaded during assembly until it is in the drive or installed position. In some systems such as a bayonet assembly the preload position is not the same as the installed or drive position as there may be an intermediate step in the assembly process that overcompresses the spring. During foldaway or breakaway the spring is further compressed to a new position. The displacement of the spring during this foldaway or breakaway compression is referred to as the working stroke. After foldaway or breakaway the mirror can then be reset to the drive position and the spring will return to the installed position.
It should be noted that the process as discussed above is true for manual and power fold systems although some power fold systems do not compress the spring during the power fold cycle but all compress the spring during a manual cycle.
The main aim or target of the spring and detent design is to achieve a minimum spring preload stroke for ease of assembly, to achieve a minimum spring damp force for mirror stability and to achieve a target spring force coupled with the detent system that gives a target breakaway torque for the mirror.
It is generally desirable, however, that once the compression of the spring has occurred to overcome the detent then the spring force applied to the pivot assembly and hence the amount of torque necessary to be applied to rotate the mirror head about the pivot assembly is a minimum at all stages so that there is minimum stress in the system during foldaway and breakaway.
Other aims are to achieve the free rotation torque requirements of the mirror and any park detent torque requirements and upon reset achieve a smooth positive re-engagement in the drive position. It is also desirable to minimise the total package size for styling freedom and reducing mirror extension away from the vehicle by allowing the glass to sweep over the top of the pivot.
In the past spring elements in mirror systems have used coil springs but these generally require a large preload stroke but during breakaway torque increases during rotation until escape is achieved but upon reset they achieve positive re-engagement in the drive position but the action is often violent. Coil springs do not minimise a total package size.
It has also been proposed to use positive spring rate disc springs and while these can minimise preload strokes during foldaway or breakaway tension increases which puts extra loads on the system and during re-engagement into the drive position the action can often be violent.
It is an object of this invention to provide a pivot system and in particular spring loading for a detent system which overcomes one or more of the problems discussed above.